combination of the word atheist and asshole. essentially, it is one who goes around looking to start arguments with theists, which he takes much pride in. they will have every counter argument for the existence of a higher power memorized better than the alphabet and will bring up the topic of religion as often as possible, especially in inappropriate situations.

person: "hi, nice to meet you."
athhole: "hey, i can't help but notice that cross your wearing. God doesn't really exist though. lol."
person: "k. see ya later." *walks away*
athhole: *yelling across the room* "there is a flying spaghetti monster in my garage. since you can't disprove it, it is true."
person: *has already started a conversation with a normal person*
athhole *to himself* "hah, sure put that douche in his place."